<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title>可以用这个方法使得属性全都有这个username</title>
	</head>
	<body>
		<script>
			class Point {
			    constructor() { }
			}
			Point.prototype.username = 'zhangsan';
			
			let p1 = new Point();
			console.log(p1.username);   //zhangsan
			
			let p2 = new Point();
			console.log(p2.username);   //zhangsan
		</script>
	</body>
</html>
